1. Field of the Invention
The present invention relates to a magnetic disc apparatus used as an information storage and in particular, to a magnetic disc apparatus including at least a vertical magnetic recording medium and a magnetoresistive (MR) head.
2. Description of the Related Art
Recently, with a progress of personal computers and workstations, a further higher density is required in the magnetic apparatus such as a hard disc drive. However, in the magnetic disc apparatus using the longitudinal magnetic recording method widely spread currently, a high recording density brings about various problems such as a problem of thermal decay of recording magnetization due to the reduced size of the recording bit and a problem of a high coercive force which may exceed the recording capability of the recording head. As means for significantly increasing the areal density while solving these problems, a study has been made on a magnetic disc apparatus using the perpendicular recording method.
FIG. 75 is a perspective view showing a conventional example of such a magnetic disc apparatus. This conventional magnetic disc apparatus includes: a perpendicular magnetic recording medium 50 supported by a rotary spindle 33; and a slider 32 having a single pole type MR composite head or an inductive (ID) MR composite head 31 positioned on a recording track 33 of the perpendicular recording media 50 and supported by an actuator 34.
FIG. 76 is a cross sectional view showing a reproduction system used in the conventional magnetic disc apparatus. This reproduction system includes a perpendicular magnetic recording medium 50 and an MR head 310. The perpendicular magnetic recording medium 50 has an undercoat soft magnetic film 52 and a perpendicular magnetization film 54 formed on a substrate 56. For example, the undercoat soft magnetic film 52 is formed using a NiFe alloy and the perpendicular magnetization film is formed using a CoCr alloy (Journal of Japan Applied Magnetism Society, Vol. 8, No. 1, 1984, p17). The magnetic recording method using the perpendicular magnetic recording medium 50 having the undercoat soft magnetic film 52 and the perpendicular magnetization film 54 is called a xe2x80x9cdouble layered perpendicular recording methodxe2x80x9d. The MR head 310 includes an MR element 313 arranged between magnetic shield layers 311 and 312 formed from a soft magnetic body. For example, the magnetic spacing d, the medium film thickness (film thickness of the perpendicular magnetization film 54) xcex4, and the reproduction gap length g are: 40 [nm], 100 [nm], and 0.2 [xcexcm], respectively.
However, the reproduction system shown in FIG. 76 is designed based on the balance relationship between the reproduction gap length, the magnetic spacing, the medium film thickness, and the like in the longitudinal recording method, not realizing the optimal specification for reproduction of the double layered perpendicular recording method. Accordingly, the reproduction resolution is not sufficient and it is difficult to perform a reproduction of a high density.
It is therefore an object of the present invention to provide a magnetic disc apparatus capable of improving a reproduction resolution at a high recording density.
The inventors of the present invention have created a simulation program associated with an MR head reproduction response in the double layered perpendicular recording method. By using this simulation program, we have designed a reproduction system of the double layered perpendicular magnetic recording method within a range of optimal values of specifications. As a result, it has been found that the conventional design value are appropriate for the longitudinal magnetic recording method but no appropriate for the double layered perpendicular magnetic recording method. For example, the reproduction gap length g has been too large for the magnetic spacing d and the medium thickness xcex4. According to the magnetic disc apparatus of the present invention, it is possible to use optimal design values obtained by simulation and by far improve the reproduction resolution as compared to the magnetic disc apparatus of the conventional double layered perpendicular magnetic recording method.
That is, the magnetic disc apparatus of the present invention includes a perpendicular magnetic recording medium and a magnetic recording/reproduction system for recording or reproducing an information onto/from the perpendicular magnetic recording medium. The perpendicular magnetic recording medium has an undercoat soft magnetic film and a vertical magnetization film. The magnetic recording/reproduction system has a single pole MR composite head consisting of a single pole head for recording and an MR head for reproduction or an inductive MR composite head consisting of an inductive head for recording and an MR head for reproduction. The magnetic disc apparatus of the present invention is characterized as follows.
In one embodiment of the invention, in the magnetic disc apparatus, a reproduction gap length as a space between a pair of magnetic shield layers sandwiching the MR head is not greater than 0.1 micrometers. In another embodiment of the invention, in the magnetic disc apparatus, when an information is reproduced with respect to the perpendicular magnetic recording medium using the single pole MR composite head or the inductive MR composite head, the magnetic spacing as a space between the single pole MR composite head or the inductive MR composite head and the perpendicular magnetic recording medium is not greater than 20 nm. In another embodiment of the invention, in the magnetic disc apparatus, the perpendicular magnetization film has a film thickness not greater than 50. In another embodiment of the invention, in the magnetic disc apparatus, the undercoat soft magnetic film has a film thickness not greater than 200 nm.
In general, the reproduction resolution is improved as the values of the reproduction gap length, the magnetic spacing, the perpendicular magnetization film thickness, and the undercoat soft magnetic film thickness are reduced below the aforementioned upper limit values. This has been confirmed by the aforementioned simulation. However, lower limit values can be set as follows. The reproduction gap length is, for example, not smaller than 0.05 [micrometers] as the limit of the current fine processing technique. The magnetic spacing is defined by the head floating amount added by a medium protection film thickness and a medium lubrication film thickness and is, for example, not less than 12 [nm]. The perpendicular magnetization film thickness is, for example, not less than 20 [nm] because when the film thickness is too small, the reproduction output is decreased, deteriorating the SN ratio. The undercoat soft magnetic film thickness is, for example, not less than 100 [nm] because when the film thickness is too small, the reproduction output is deteriorated.
Moreover, the undercoat soft magnetic film is preferably formed from FeSiAl or FeSiAl-containing alloy, CoNiFe or CoNiFe-containing alloy, CoZrTa, CoZrNb alloy, or the like. The perpendicular magnetization film is preferably formed from CoCrM alloy (wherein M is Tb, Dy, Ho, Er, or Tm), FePt alloy or FePt-containing alloy, RCo5 (wherein R is Y, Ce, Sm, La, or Pr), R2Co17 (wherein R is Y, Ce, Sm, La, or Pr)